Communication device and communication method

ABSTRACT

[Solution] Provided is a communication device including: a selection unit configured to select a synchronization signal from respective synchronization signals received from two or more other devices on a basis of origin information that is acquired by communication with another device and that indicates an origin of a synchronization signal used for acquisition of synchronization timing in the other device; and a synchronization processing unit configured to acquire synchronization timing using the synchronization signal selected by the selection unit.

TECHNICAL FIELD

The present disclosure relates to a communication device and acommunication method.

BACKGROUND ART

By utilizing a communication device onboard a mobile object such as avehicle, direct communication between the mobile object and varioustarget objects is realized. Communication between a communication deviceonboard a mobile object and various other communication devices iscalled vehicle-to-X (V2X) communication. For V2X communication,communication systems utilizing dedicated short range communications(DSRC) have been investigated thus far, but recently, investigation intocommunication systems utilizing mobile phone communication standardssuch as Long Term Evolution (LTE) is progressing. Note that a systemrelated to the LTE communication standard is disclosed in PatentLiterature 1 below, for example.

CITATION LIST Patent Literature

Patent Literature 1: WO 13/080764

DISCLOSURE OF INVENTION Technical Problem

In the above V2X communication, the communication device onboard themobile object may conduct a synchronization process using several typesof synchronization signals. For example, the communication deviceonboard the mobile object may conduct a synchronization process using asynchronization signal transmitted from an LTE base station, or asynchronization signal transmitted from a communication device onboardanother mobile object. However, among synchronization signals, the areasin which each synchronization signal is used and the accuracy of eachsynchronization signal are expected to be different. For this reason,innovation is desired with respect to which synchronization signal acommunication device uses to conduct the synchronization process.

Solution to Problem

According to the present disclosure, there is provided a communicationdevice including: a selection unit configured to select asynchronization signal from respective synchronization signals receivedfrom two or more other devices on a basis of origin information that isacquired by communication with another device and that indicates anorigin of a synchronization signal used for acquisition ofsynchronization timing in the other device; and a synchronizationprocessing unit configured to acquire synchronization timing using thesynchronization signal selected by the selection unit.

In addition, according to the present disclosure, there is provided acommunication device including: a synchronization processing unitconfigured to acquire synchronization timing on a basis of reception ofa synchronization signal; and a control unit configured to controltransmission of the synchronization signal after the acquisition of thesynchronization timing by the synchronization processing unit. Thecontrol unit further controls transmission of origin information thatindicates an origin of the synchronization signal used for theacquisition of the synchronization timing.

In addition, according to the present disclosure, there is provided acommunication method including: selecting, by a processor, asynchronization signal from respective synchronization signals receivedfrom two or more other devices on a basis of origin information that isacquired by communication with another device and that indicates anorigin of a synchronization signal used for acquisition ofsynchronization timing in the other device; and acquiringsynchronization timing using the selected synchronization signal.

In addition, according to the present disclosure, there is provided acommunication method including: acquiring synchronization timing on abasis of reception of a synchronization signal; controlling transmissionof a synchronization signal after the acquisition of the synchronizationtiming; and controlling, by a processor, transmission of origininformation that indicates an origin of a synchronization signal usedfor the acquisition of the synchronization timing.

Advantageous Effects of Invention

According to the present disclosure, as explained above, it is possibleto realize innovation with respect to which synchronization signal acommunication device uses to conduct the synchronization process. Notethat the effects described above are not necessarily limited, and alongwith or instead of the effects, any effect that is desired to beintroduced in the present specification or other effects that can beexpected from the present specification may be exhibited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram for describing an overview of V2Xcommunication.

FIG. 2 is an explanatory diagram illustrating a configuration of awireless communication system according to an embodiment of the presentdisclosure.

FIG. 3 is an explanatory diagram illustrating an example of D2Dcommunication modes.

FIG. 4 is an explanatory diagram illustrating control of D2Dcommunication by an eNB.

FIG. 5 is an explanatory diagram illustrating a configuration of a UEand an eNB according to an embodiment of the present disclosure.

FIG. 6 is an explanatory diagram illustrating synchronization conditionsnear a tunnel.

FIG. 7 is an explanatory diagram illustrating a flow of a process of afirst operation example.

FIG. 8 is an explanatory diagram illustrating another flow of a processof a first operation example.

FIG. 9 is an explanatory diagram illustrating a specific example ofcommunication modes in a wireless communication system.

FIG. 10 is a flowchart illustrating a diagrammatic process flow of asecond operation example.

FIG. 11 is an explanatory diagram illustrating an operation example in acase in which the synchronized states of multiple UEs are lost aroundthe same time.

FIG. 12 is an explanatory diagram illustrating an operation example in acase in which the synchronized states of multiple UEs are lost aroundthe same time.

FIG. 13 is an explanatory diagram illustrating an operation example in acase in which the synchronized states of multiple UEs are lost aroundthe same time.

FIG. 14 is an explanatory diagram illustrating a specific example of anoffset value.

FIG. 15 is an explanatory diagram illustrating several methods by whichan eNB or an RSU acquires an offset value.

FIG. 16 is a block diagram illustrating a first example of a schematicconfiguration of an eNB.

FIG. 17 is a block diagram illustrating a second example of a schematicconfiguration of an eNB.

FIG. 18 is a block diagram illustrating an example of a schematicconfiguration of a smartphone.

FIG. 19 is a block diagram illustrating an example of a schematicconfiguration of a car navigation device.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. Notethat in this specification and the appended drawings, structuralelements that have substantially the same function and structure aredenoted with the same reference numerals, and repeated explanation ofthese structural elements is omitted.

Also, in this specification and the appended drawings, multiplestructural elements having substantially the same function and structuremay in some cases be distinguished by different letters appended to thesame sign. For example, multiple elements having substantially the samefunction and structure or logical significance are distinguished as UEs20A, 20B, 20C, and so on as necessary. On the other hand, in a case ofnot particularly distinguishing each of multiple structural elementshaving substantially the same function and structure, only the same signwill be given. For example, in a case of not particularly distinguishingUEs 20A, 20B, and 20C, each of the UEs 20A, 20B, and 20C will bedesignated simply the UE 20.

In addition, the present disclosure will be described in the orderindicated below.

0. Introduction

1. Overview of wireless communication system

2. Configuration of UE and eNB

3. Operation examples

3-1. First operation example

3-2. Second operation example

3-3. Third operation example

4. Applications

5. Conclusion

0. INTRODUCTION

By utilizing a communication device onboard a mobile object such as avehicle, direct communication between the mobile object and varioustarget objects is realized. Communication between a vehicle and varioustarget objects is called vehicle-to-X (V2X) communication. FIG. 1 is anexplanatory diagram for describing an overview of V2X communication. Asillustrated in FIG. 1, V2X communication may be vehicle-to-vehicle (V2V)communication, vehicle-to-infrastructure (V2I) communication,vehicle-to-pedestrian (V2P) communication, or vehicle-to-home (V2H)communication, for example.

As illustrated in FIG. 1, the communication target of a vehicle in V2Vcommunication may be a passenger vehicle, a commercial or fleet vehicle,an emergency vehicle, or a transit vehicle, for example. Also, thecommunication target of a vehicle in V2I communication may be a cellularnetwork, a data centre, a fleet or freight management centre, a trafficmanagement centre, a weather service, a rail operation centre, a parkingsystem, or a toll system, for example. Also, the communication target ofa vehicle in V2P communication may be a cyclist, a pedestrian shelter,or a motorcycle, for example. Also, the communication target of avehicle in V2H communication may be a home network, a garage, orenterprise or dealer networks, for example.

Note that in V2X communication, communication systems utilizingdedicated short range communications (DSRC) have been investigated, butrecently, investigation into communication systems utilizing mobilephone communication standards such as Long Term Evolution (LTE) isprogressing.

Examples of applications of V2X communication include communicationsystems intended for forward collision warning, loss of control warning,emergency vehicle warning, emergency stop, adaptive cruise assist,traffic condition warning, traffic safety, automatic parking, routedeviation warning, message transmission, collision warning,communication range extension, traffic volume optimization, curve speedalert, pedestrian collision warning, vulnerable person safety, or thelike.

The following describes a wireless communication system for conductingcommunication between User Equipment (UE), which are communicationdevices onboard vehicles, as such V2X communication.

1. OVERVIEW OF WIRELESS COMMUNICATION SYSTEM

FIG. 2 is an explanatory diagram illustrating a configuration of awireless communication system according to an embodiment of the presentdisclosure. As illustrated in FIG. 2, the wireless communication systemaccording to an embodiment of the present disclosure includes a UE 20, avehicle 22, an eNB 30, a GPS satellite 40, and a roadside unit (RSU) 50.

The eNB 30 is a cellular base station that provides a cellularcommunication service to the UE 20 positioned inside a cell. Forexample, the eNB 30 schedules resources for the UE 20 to communicate by,and notifies the UE 20 of the scheduled resources. Additionally, the eNB30 conducts uplink communication or downlink communication with the UE20 in the relevant resources.

The GPS satellite 40 is an artificial satellite (communication device)that circles around the earth following a certain orbit. The GPSsatellite 40 transmits a Global Navigation Satellite System (GNSS)signal including a navigation message. The navigation message includesvarious information for position estimation, such as orbit informationand time information of the GPS satellite 40.

The RSU 50 is a communication device installed on the roadside. The RSU50 is able to communicate bidirectionally with the vehicle 22 or the UE20 onboard the vehicle 22. Note that the RSU 50 may conduct DSRCcommunication with the vehicle 22 or the UE 20 onboard the vehicle 22,but in the present embodiment, it is anticipated that the RSU 50 alsocommunicates with the vehicle 22 or the UE 20 onboard the vehicle 22according to a cellular communication method.

The UE 20 is a communication device installed onboard the vehicle 22,and moves as the vehicle 22 travels. The UE 20 has a function ofcommunicating with the eNB 30 under control by the eNB 30. Additionally,the UE 20 has a function of receiving the GNSS signal transmitted fromthe GPS satellite 40, and estimating position information of the UE 20from the navigation message included in the GNSS signal. The UE 20 alsohas a function of communicating with the RSU 50. Furthermore, the UE 20according to the present embodiment is also capable of communicatingdirectly with a UE 20 onboard another vehicle 22, or in other words,conducting device-to-device (D2D) communication discussed later.

Note that although FIG. 2 illustrates the vehicle 22 as an example of amobile object, the mobile object is not limited to the vehicle 22. Forexample, the mobile object may also be an object such as a marinevessel, an aircraft, or a bicycle. In addition, although the abovedescribes the UE 20 as including the function of receiving the GNSSsignal, the vehicle 22 may have the function of receiving the GNSSsignal, and the vehicle 22 may output a GNSS signal reception result tothe UE 20.

(D2D Communication)

At this point, among the elemental technologies used in the wirelesscommunication system discussed above, D2D communication as it relatesparticularly to an embodiment of the present disclosure will bedescribed more specifically.

—Overview—

D2D communication is direct communication between UEs 20 without goingthrough the eNB 30, for example, and is standardized in 3GPP Release 12.In D2D communication, two communication methods called “Discovery” and“Communication” are supported. “Discovery” is communication used by a UE20 to notify nearby equipment of the existence of the UE 20, and thedata size in “Discovery” is fixed. On the other hand, “Communication”realizes communication using a control signal and a data signal betweenUEs 20. Such D2D is standardized for public safety purposes, but theusage of D2D is not limited to public safety, and the application of D2Dto SNS, game, M2M, automotive scenarios, and the like is also expected.

—Communication Modes—

In D2D, various communication modes are anticipated. For example, acommunication mode in which both UEs 20 conducting D2D communication areincluded in a coverage C is called “In-coverage”, while a communicationmode in which one of the UEs 20 conducting D2D communication is includedin the coverage C is called “Partial-coverage”, and a communication modein which both of the UEs 20 conducting D2D communication are notincluded in the coverage C is called “Out-of-coverage”. A specificexample regarding this point will be described with reference to FIG. 3.

FIG. 3 is an explanatory diagram illustrating an example of D2Dcommunication modes. In the example illustrated in FIG. 3, UEs 20A, 20B,and 20C are positioned inside the coverage C of the eNB 30, while UEs20D, 20E, and 20F are positioned outside the coverage C of the eNB 30.Herein, since both the UEs 20A and 20B are included in the coverage C,the D2D communication conducted by the UEs 20A and 20B is “In-coverage”.Since only the UE 20C is included in the coverage C, the D2Dcommunication conducted by the UEs 20C and 20D is “Partial-coverage”.Since both the UEs 20E and 20F are not included in the coverage C, theD2D communication conducted by the UEs 20E and 20F is “Out-of-coverage”.

In “In-coverage” or “Partial-coverage”, the UE 20 is able to conduct D2Dcommunication under control by the eNB 30. On the other hand, in“Out-of-coverage”, the UE 20 realizes D2D communication without controlby the eNB 30.

Note that although the above illustrates one-to-one communication modes,the communication modes in D2D are not limited to being one-to-one. Forexample, in D2D, besides one-to-one communication modes called “UnicastCommunication”, one-to-many communication modes called names such as“Broadcast Communication” and “Group Cast Communication” are alsosupported.

—Communication Control—

In “In-coverage” or “Partial-coverage”, D2D communication between UEs 20is controlled according to a control signal transmitted from the eNB 30.The control of D2D communication by the eNB 30 will be described withreference to FIG. 4.

FIG. 4 is an explanatory diagram illustrating control of D2Dcommunication by the eNB 30. As illustrated in FIG. 4, resources for D2Dcommunication are mapped by time-division with resources for LTE uplink,as illustrated in FIG. 4. The resources for D2D communication arepartitioned in units called resource pools, and “Discovery” or“Communication” is conducted inside each resource pool. As illustratedin FIG. 4, a discovery signal is transmitted in the resource pool for“Discovery”, while a data signal and a control signal for controllingthe communication of the data signal are transmitted in the resourcepool for “Communication”. Note that the above discovery signal, controlsignal, and data signal are defined as the Physical Sidelink DiscoveryChannel (PSDCH), the Physical Sidelink Control Channel (PSCCH), and thePhysical Sidelink Shared Channel (PSSCH), respectively.

On the other hand, in “Out-of-coverage”, since the control signal fromthe eNB 30 does not reach either of the UEs 20 conducting D2Dcommunication, the UE 20 conducts D2D communication using parameterspreset in the UE 20.

—Synchronization—

Multiple UEs 20 are able to conduct D2D communication by synchronizingwith each other. The synchronization signals used for thesynchronization of the UE 20 may be the Primary Sidelink SynchronizationSignal (PSSS) and the Secondary Sidelink Synchronization Signal (SSSS).The synchronization signal is mapped across six resource blocks of thecenter frequency with a 40 ms period. Near the synchronization signal,signals such as the Physical Sidelink Broadcast Channel (PSBCH) and theDemodulation Reference Signal (DMRS) are also mapped. Note thatpriorities on the usage of synchronization signals are defined asfollows.

1. eNBs that meet the Scriterion

2. UEs within network coverage*

3. UEs out of network coverage transmitting D2DSS from D2DSSue_net*

4. UEs out of network coverage transmitting D2DSS from D2DSSue_oon*

If none of the above are selected, the UE uses its own internal clock.

2. CONFIGURATION OF UE AND ENB

The above thus describes an overview of a wireless communication systemaccording to an embodiment of the present disclosure. Next, FIG. 5 willbe referenced to describe a configuration of the UE 20 and the eNB 30included in the wireless communication system.

FIG. 5 is an explanatory diagram illustrating a configuration of the UE20 and the eNB 30 according to an embodiment of the present disclosure.As illustrated in FIG. 5, the UE 20 is equipped with a communicationunit 210, a GNSS signal processing unit 220, a storage unit 230, aselection unit 240, a synchronization processing unit 250, and a controlunit 260. Also, the eNB 30 is equipped with a communication unit 310, astorage unit 330, and a control unit 360.

(UE 20)

The communication unit 210 of the UE 20 is an interface with othercommunication devices, and communicates various signals with othercommunication devices. For example, the communication unit 210 receivessignals such as the synchronization signal, the control signal, and thedata signal from the eNB 30. Note that the communication unit 210 isalso capable of communicating with other UEs 20 and the RSU 50. For thisreason, the communication unit 210 may receive synchronization signalsfrom multiple communication devices such as other UEs 20, the eNB 30,and the RSU 50.

The GNSS signal processing unit 220 processes a GNSS signal transmittedfrom the GPS satellite 40. For example, the GNSS signal processing unit220 processes the GNSS signal to thereby estimate position informationand time information of the UE 20. Note that the synchronizationprocessing unit 250 discussed later is also capable of conducting asynchronization process based on time information estimated from theGNSS signal, and thus in the present disclosure, the GNSS signal or thetime information included in the GNSS signal is also treated as asynchronization signal.

The storage unit 230 stores information used in operations of the UE 20.For example, the storage unit 230 may store information such asparameters and programs used for control by the control unit 260, andmap information indicating geographical features and road layouts.

The selection unit 240 selects a synchronization signal to be used forthe synchronization process from among one or multiple synchronizationsignals received from other communication devices. The inventor of thepresent disclosure made innovations particularly with respect to thedesign of the selection unit 240 so that a suitable synchronizationsignal is selected in the selection unit 240, and as a result, devisedseveral designs of the selection unit 240. These several designs of theselection unit 240 will be described specifically and in detail in <3.Operation examples>.

The synchronization processing unit 250 conducts a synchronizationprocess based on the synchronization signal selected by the selectionunit 240, and acquires synchronization timings. As a result, the UE 20becomes synchronized with the device that transmitted thesynchronization signal, thereby enabling the UE 20 to conduct D2Dcommunication with the device that transmitted the synchronizationsignal.

The control unit 260 controls overall operation of the UE 20. Forexample, after the synchronization process is conducted by thesynchronization processing unit 250, or if no synchronization signal isreceived, the control unit 260 controls the transmission of asynchronization signal by the communication unit 210.

(eNB 30)

The communication unit 310 of the eNB 30 is an interface with othercommunication devices, and communicates various signals with othercommunication devices. For example, the communication unit 310 transmitssignals such as the synchronization signal, the control signal, and adownlink data signal to the UE 20, and receives an uplink data signalfrom the UE 20. Also, similarly with the RSU 50, the communication unit310 is also able to transmit signals such as the synchronization signal,the control signal, and a downlink data signal to the RSU 50, andreceive an uplink data signal from the RSU 50.

The storage unit 330 stores information used in operations of the eNB30. For example, the storage unit 330 may store information such asparameters and programs used for control by the control unit 360, andmap information indicating geographical features and road layouts.

The control unit 360 controls overall operation of the eNB 30. Forexample, the control unit 360 performs various controls, such as afunction of allocating resources to the UE 20, random access control,paging control, and transmission of power control.

3. OPERATION EXAMPLES

Hereinafter, a configuration of the UE 20 and the eNB 30 according to anembodiment of the present disclosure will be described. Subsequently,operation examples according to an embodiment of the present disclosurewill be described successively in detail.

3-1. First Operation Example

—Introduction—

The UE 20 onboard the vehicle 22 moves as the vehicle 22 travels. Forthis reason, the type of device that transmits a synchronization signalreceivable by the UE 20 changes as the vehicle 22 travels. For example,in an unshielded area, the UE 20 may receive the GNSS signal(synchronization signal) from the GPS satellite 40. Also, in anunshielded area which is also inside the cell of the eNB 30, the UE 20may also receive a synchronization signal from the eNB 30. On the otherhand, in a shielded area, another UE 20 may transmit a synchronizationsignal due to the other UE 20 being unable to receive a synchronizationsignal from either the eNB 30 or the GPS satellite 40, and in this case,the UE 20 may receive a synchronization signal from the other UE 20.Furthermore, near the border between an unshielded area and a shieldedarea, the UE 20 may receive a synchronization signal from any of the GPSsatellite 40, the eNB 30, and the other UE 20.

Herein, the shielded area above may be a tunnel or an undergroundpassage, for example. Accordingly, for the sake of a more specificunderstanding, the synchronization conditions near a tunnel will bedescribed with reference to FIG. 6.

FIG. 6 is an explanatory diagram illustrating synchronization conditionsnear a tunnel. In the example illustrated in FIG. 6, the UEs 20B and 20Care moving inside the tunnel, the UE 20A is coming out of the tunnel,and the UEs 20D and 20E are proceeding into the tunnel. At this point, asynchronization signal from either the eNB 30 or the GPS satellite 40does not reach the UEs 20B and 20C moving inside the tunnel, and thusD2D communication between the UEs 20 20B and 20C is realized by the UE20B or 20C transmitting a synchronization signal, as illustrated in FIG.6. Also, synchronization signals from the eNB 30 and the GPS satellite40 reach the UEs 20D and 20E, and thus FIG. 6 illustrates an example inwhich the UEs 20D and 20E conduct D2D communication by using thesynchronization signal from the eNB 30 or the GPS satellite 40.

However, the UE 20D positioned near the boundary of the tunnel isincluded in the coverage 24C of the synchronization signal transmittedby the UE 20C, and thus the UE 20D is also able to receive thesynchronization signal from the UE 20C. Similarly, the UE 20A positionednear the boundary of the tunnel is included in the coverage 24B of thesynchronization signal transmitted by the UE 20B, and thus the UE 20A isable to receive synchronization signals from the GPS satellite 40, theeNB 30, and the UE 20B.

In this way, in a case where synchronization signals are received frommultiple types of devices, it is desirable to appropriately select thesynchronization signal to be used in the synchronization process.Hereinafter, as a first operation example, an operation forappropriately selecting a synchronization signal in a case wheresynchronization signals are received from multiple types of devices willbe described. Note that in the following description of the firstoperation example, the UE 20 will be described as a device of the firsttype, while the eNB 30 or the GPS satellite 40 related to a system thatprovides a service in a wider range than the device of the first typedoes will be described as a device of the second type.

—Main Issue—

According to one perspective, to enable the UE 20 to conduct D2D with alarger number of other UEs 20, it is desirable to synchronize to aglobal synchronization signal transmitted by the eNB 30 or the GPSsatellite 40, rather than a local synchronization signal transmitted byanother UE 20. However, if the UE 20 enters a tunnel, the globalsynchronization signal no longer reaches, and thus synchronizationbecomes unstable temporarily until synchronization is conducted with alocal synchronization signal.

Accordingly, the selection unit 240 of the UE 20 according to thepresent operation example selects a synchronization signal based on adetermination of whether or not the movement of the UE 20 is proceedingtoward an area where the synchronization signals from the eNB 30 and theGPS satellite 40 do not reach. For example, if the movement of the UE 20is proceeding toward an area where the synchronization signals from theeNB 30 and the GPS satellite 40 do not reach, the selection unit 240 mayselect a local synchronization signal transmitted by another UE 20.According to such a configuration, it is possible to ensure thestability of synchronization, even when the movement of the UE 20arrives at the above area. On the other hand, if the movement of the UE20 is proceeding out of an area where the synchronization signal fromthe eNB 30 or the GPS satellite 40 does not reach, the selection unit240 may select a global synchronization signal transmitted by the eNB 30or the GPS satellite 40. According to such a configuration, it ispossible to change from the selection of a local synchronization signalto the selection of a global synchronization signal at an earlier pointin time. In this way, the gist of the present operation example is thatin a case where the UE 20 is positioned in a region containing both alocal synchronization signal and a global synchronization signal, the UE20 does not select a synchronization signal rigidly, but instead selectsa synchronization signal appropriately according to the movementconditions of the UE 20. Hereinafter, this point will be described morespecifically with the example of FIG. 6.

In the example illustrated in FIG. 6, the UE 20A and the UE 20D arepositioned in a region containing both a local synchronization signaland a global synchronization signal. At this point, the UE 20D isproceeding into the tunnel, which is an example of an area where thesynchronization signals from the eNB 30 and the GPS satellite 40 do notreach. Accordingly, the selection unit 240 of the UE 20D may select thelocal synchronization signal transmitted by the other UE 20C. Meanwhile,the UE 20A is coming out of the tunnel. Accordingly, the UE 20A mayselect the global synchronization signal transmitted by the eNB 30 orthe GPS satellite 40, so as to be able to conduct D2D communication witha larger number of other UEs 20.

Herein, the determination of whether or not the UE 20 is proceeding intoa tunnel may be conducted by a variety of agents. Additionally, thedetermination of whether or not the UE 20 is proceeding into a tunnelmay be conducted by a variety of techniques. Hereinafter, severalexamples will be described for the flow of a process that includes adetermination of whether or not the UE 20 is proceeding into a tunnel.

—Details—

1)

First, FIG. 7 will be referenced to describe the flow of a process in acase in which the eNB 30 makes the determination of whether or not theUE 20 is proceeding into a tunnel. Note that the process of the eNB 30illustrated in FIG. 7 may also be conducted by the RSU 50.

FIG. 7 is an explanatory diagram illustrating a flow of a process of thefirst operation example. As illustrated in FIG. 7, first, the GNSSsignal processing unit 220 of the UE 20 acquires position information(S404), and the communication unit 210 of the UE 20 transmits theposition information of the UE 20 to the eNB 30 (S408). Note that theposition information of the UE 20 may also be acquired by a GNSS signalprocessing unit provided in the vehicle 22.

The control unit 360 of the eNB 30 determines, based on the positioninformation received from the UE 20, whether or not the UE 20 ispositioned in a region containing both a local synchronization signaland a global synchronization signal, such as whether or not the UE 20 ispositioned near a tunnel, for example (S412). The control unit 360 maymake the determination by referencing map information stored in thestorage unit 330. At this point, if it is determined that the UE 20 isnot positioned near a tunnel (S412/no), the eNB 30 does not transmit anyparticular instruction about a synchronization signal to the UE 20.

On the other hand, if it is determined that the UE 20 is positioned neara tunnel (S412/yes), the eNB 30 instructs the UE 20 to select a localsynchronization signal if the movement of the UE 20 is proceeding intothe tunnel (S416/yes, S420). Conversely, the eNB 30 instructs the UE 20to select a global synchronization signal if the movement of the UE 20is proceeding out of the tunnel (S424/yes, S428). Note that the eNB 30may issue the above instruction in the SIB or the DCI of a Uu link.

Subsequently, the selection unit 240 of the UE 20 selects asynchronization signal according to the instruction from the eNB 30(S432), and the synchronization processing unit 250 of the UE 20conducts the synchronization process using the synchronization signalselected by the selection unit 240 (S436).

2)

Next, FIG. 8 will be referenced to describe the flow of a process in acase in which the UE 20 itself makes the determination of whether or notthe UE 20 is proceeding into a tunnel.

FIG. 8 is an explanatory diagram illustrating another flow of a processof the first operation example. As illustrated in FIG. 8, first, theGNSS signal processing unit 220 of the UE 20 acquires positioninformation (S440), and the selection unit 240 determines whether or notthe UE 20 is positioned in a region containing both a localsynchronization signal and a global synchronization signal, such aswhether or not the UE 20 is positioned near a tunnel, for example(S444). The selection unit 240 may make the determination by referencingmap information (local dynamic mapping (LDM), for example) stored in thestorage unit 230. At this point, if it is determined that the UE 20 isnot positioned near a tunnel, the selection unit 240 maintains theselection of the currently selected synchronization signal.

On the other hand, if it is determined that the UE 20 is positioned neara tunnel (S444/yes), the selection unit 240 selects a localsynchronization signal if the movement of the UE 20 is proceeding intothe tunnel (S448/yes, S452). Conversely, the selection unit 240 selectsa global synchronization signal if the movement of the UE 20 isproceeding out of the tunnel (S456/yes, S460). The synchronizationprocessing unit 250 of the UE 20 conducts the synchronization processusing the synchronization signal selected by the selection unit 240(S464).

3)

Furthermore, the eNB 30 provides the UE 20 with information forselecting a synchronization signal in the UE 20, and the selection unit240 of the UE 20 may select a synchronization signal based on thisinformation. In other words, the UE 20 may provide position informationto the eNB 30, and the eNB 30 may determine factors such as whether ornot the UE 20 is proceeding into a tunnel as discussed above, anddepending on the determination result, provide the UE 20 withinformation for selecting a synchronization signal in the UE 20. Theinformation for selecting a synchronization signal may be informationsuch as received signal strength bias information, changeoverprobability, and priority table information. For example, if theselection of a local synchronization signal is desired, the eNB 30 mayset the received signal strength bias information, which is used by theUE 20 to determine if the reception of the synchronization signal wassuccessful, to a high level for the global synchronization signal and toa low level for the local synchronization signal, and notify the UE 20of the set bias information. Alternatively, in a case in which the UE 20generates a random number and changes the synchronization signal in acase where the random number exceeds a threshold value, the eNB 30 maytransmit information indicating the above threshold value to the UE 20as a changeover probability. Alternatively, if the selection of a localsynchronization signal is desired, the eNB 30 may transmit to the UE 20a priority table indicating a higher priority for the localsynchronization signal than the global synchronization signal.

4)

Also, as a modification, the RSU 50 that transmits a synchronizationsignal changeover instruction may be installed near the entrance andalso near the exit of an area such as a tunnel or an undergroundpassage. For example, the RSU 50 near the entrance of the area mayperiodically broadcast a changeover signal for changing over to a localsynchronization signal, while the RSU 50 near the exit of the area mayperiodically broadcast a changeover signal for changing over to a globalsynchronization signal. According to such a configuration, smoothchangeover of the synchronization signal may be realized without makinga software-based determination based on position information in the eNB30 or the UE 20.

In addition, the movement conditions of the UE 20 may also be determinedbased on a lane ID indicating which road the UE 20 is moving along. TheUE 20 or the vehicle 22 transmits position information to the eNB 30,and may receive a lane ID corresponding to the position information fromthe eNB 30, or receive a lane ID from the RSU 50. Also, the movementconditions of the UE 20 may also be determined from an RARP or RSRQmeasurement value of the eNB 30 in the UE 20. For example, if theRSRP/RSRQ is smaller than a certain threshold value, it may bedetermined that the UE 20 is about to go outside the network (enter thetunnel). Additionally, the movement conditions of the UE 20 may also bedetermined from the magnitude of change (degradation) in the RSRP/RSRQ.For example, if a sustained degradation in the RSSP/RSRQ can beconfirmed, it may be determined that the UE 20 is heading outside thenetwork.

3-2. Second Operation Example

The above thus describes a first operation example according to anembodiment of the present disclosure. Next, a second operation exampleaccording to an embodiment of the present disclosure will be described.The second operation example is an example in which a synchronizationsignal is selected from among multiple synchronization signals based onthe origin of each synchronization signal. Hereinafter, an overview ofthe second operation example will be described, and then the secondoperation example will be described in detail.

—Introduction—

If a communication device acquires synchronization timings based on asynchronization signal transmitted from another communication device,the communication device may transmit a synchronization signal inaccordance with the synchronization timings. Furthermore, based on thesynchronization signal transmitted by this communication device, yetanother downstream communication device may acquire synchronizationtimings. This relaying of synchronization timings via synchronizationsignals will be described specifically with reference to FIG. 9.

FIG. 9 is an explanatory diagram illustrating a specific example ofcommunication modes in a wireless communication system. In the exampleillustrated in FIG. 9, the UE 20A receives a synchronization signal fromthe UE 20B which acts as a source device (the source of thesynchronization signal and synchronization timings). The UE 20A acquiressynchronization timings based on the synchronization signal, andtransmits the synchronization signal, while the UE 20E uses thesynchronization signal transmitted from the UE 20A to acquiresynchronization timings. At this point, the UEs 20A, 20B, and 20E sharesynchronization timings. In other words, the synchronization timingsoriginating from the UE 20B may be considered to be relayed to the UE20E by the UE 20A.

Also, in the example illustrated in FIG. 9, the UE 20C receives asynchronization signal from the eNB 30 which acts as a source device,acquires synchronization timings based on the synchronization signal,and transmits a synchronization signal. Additionally, the UE 20D usesthe synchronization signal transmitted from the UE 20C to acquiresynchronization timings. At this point, the UE 20D is positioned outsidethe radio coverage of the eNB 30, but is able to acquire thesynchronization timings of the eNB 30 that acts as a source devicethrough the interposition of UE 20C.

Also, in the example illustrated in FIG. 9, the UE 20F receives asynchronization signal (GNSS signal) from the GPS satellite 40 whichacts as a source device, acquires synchronization timings based on thesynchronization signal, and transmits a synchronization signal.Additionally, the UE 20G uses the synchronization signal transmittedfrom the UE 20F to acquire synchronization timings. In other words, theUE 20G acquires the synchronization timings of the GPS satellite 40 thatacts as a source device.

However, each UE 20 may receive multiple synchronization signals fromdifferent types of source devices. For example, the UE 20E illustratedin FIG. 9 may receive a synchronization signal from another UE acting asa source device (the UE 20B), as well as a synchronization signal fromthe eNB 30 acting as a source device, and a synchronization signal fromthe GPS satellite 40 acting as a source device.

For this reason, it is desirable to appropriately select thesynchronization signal to be used in the synchronization process fromamong multiple synchronization signals from different types of sourcedevices. Hereinafter, as a second operation example, an operation forappropriately selecting a synchronization signal to be used in thesynchronization process from among multiple synchronization signals fromdifferent types of source devices will be described. Note that in thefollowing description of the second operation example, the eNB 30 willbe described as a device of the first type, while the GPS satellite 40related to a system that provides a service in a wider range than thedevice of the first type does will be described as a device of thesecond type.

—Main Issue—

As also described in the first operation example, according to oneperspective, to enable the UE 20 to conduct D2D with a larger number ofother UEs 20, it is desirable to operate according to thesynchronization timings of the eNB 30 or the GPS satellite 40 acting asthe source device. However, it is difficult to ascertain the sourcedevice from information indicating the immediately previous device thattransmitted the synchronization signal.

For this reason, in a case where a communication device such as the UE20 or the RSU 50 according to the present operation example acquiressynchronization timings based on the reception of a synchronizationsignal from another communication device, and transmits asynchronization signal in accordance with these synchronization timings,origin information indicating the origin of the synchronization signalused to acquire the synchronization timings is transmitted.Additionally, a communication device receiving multiple synchronizationsignals selects a synchronization signal based on the origin informationcorresponding to each synchronization signal. According to such aconfiguration, even if the UE 20 receives multiple synchronizationsignals from different types of source devices, the UE 20 is able toselect a synchronization signal appropriately. Hereinafter, adiagrammatic process flow will be described with reference to FIG. 10,and then a specific example of origin information and a specific exampleof the selection of a synchronization signal using origin informationwill be described.

FIG. 10 is a flowchart illustrating a diagrammatic process flow of asecond operation example. As illustrated in FIG. 10, first, thecommunication unit 210 of the UE 20 scans for synchronization signals(S504). If a synchronization signal is not discovered by the scan(S508/no), the control unit 260 of the UE 20 decides that the UE 20itself will be a source device, and controls the transmission of asynchronization signal from the communication unit 210 (S510).

On the other hand, if synchronization signals are discovered by the scan(S508/yes), the selection unit 240 extracts synchronization signalshaving a quality equal to or greater than a threshold value (S512). Atthis point, the selection unit 240 may also use origin information toextract synchronization signals having a quality equal to or greaterthan a threshold value. The determination of whether or not the qualityis equal to or greater than a threshold value may be a determination ofwhether or not the number of interposing devices in the procedure ofrelaying synchronization timings discussed later exceeds a certainnumber, for example.

In S512, if no synchronization signal having a quality equal to orgreater than a threshold value is extracted (S516/no), the control unit260 of the UE 20 decides that the UE 20 itself will be a source device,and controls the transmission of a synchronization signal from thecommunication unit 210 (S510). Also, if only one synchronization signalhaving a quality equal to or greater than a threshold value is extracted(S516/yes, S520/no), the selection unit 240 selects the extractedsynchronization signal. On the other hand, if multiple synchronizationsignals having a quality equal to or greater than a threshold value areextracted (S520/yes), the selection unit 240 uses origin information toselect a higher-priority synchronization signal (S528). Subsequently,the synchronization processing unit 250 acquires synchronization timingsusing the synchronization signal selected by the selection unit 240(S532).

—Origin Information—

Origin information is information indicating the origin of asynchronization signal used to acquire synchronization timings. Theorigin information includes information depending on the source deviceof the synchronization signal. For example, the origin information mayinclude information indicating the type of source device, such as a GPSsatellite, an eNB, an RSU, or a UE. Alternatively, the origininformation may include identification information unique to the sourcedevice, such as a GNSS_ID, a cell ID, an Encrypted Mobile SubscriberIdentity (EMSI), or a Radio Network Temporary ID (RNTI).

Furthermore, the origin information may include various informationrelated to the origin of the synchronization signal. For example, theorigin information may also include information indicating the procedureof relaying synchronization timings from the source device to thecommunication device that transmitted the synchronization signal. Theinformation indicating the procedure of relaying synchronization timingsmay be number-of-interpositions information indicating the number ofinterposing devices in the above relaying procedure, informationindicating the interposing devices in the above relaying procedure, orthe like.

For example, the origin information may be expressed as (number ofinterposing devices: n)(source device)(interposing devices (n devices)).For example, if the number of interposing devices is 3, the sourcedevice is a GPS satellite (identity: 0), and an RSU (identity: 2) and aUE (identity: 3) are interposing, the origin information may be a bitmap expressed as (3, 0, 2, 3)=11001011. Note that the origin informationmay also include communication type information, such as D2D publicsafety, D2D commercial, V2V, V2I, or V2P.

The method of transmitting the above origin information is notparticularly limited. For example, the UE 20 may transmit origininformation as system information regarding the PSBCH. Alternatively,the UE 20 may use information indicating the type of source device,which is an example of origin information, as a seed for generating asynchronization signal. For example, in the D2D communication mode, theUE 20 may use information indicating the type of source device as an IDfor generating the SSSS. Alternatively, the UE 20 may use informationindicating the type of source device as the root index of the PSSS. Forreference, methods of generating the PSSS and the SSSS are indicatedbelow. In a case where information indicating the type of source deviceis used as an ID for generating the SSSS, the information indicating thetype of source device may be used as NID(1) and NID(2) below.

[Math. 1] PSSS  Sequence   New root index u {26, 37}    PD2DSSue_net: 26   PD2DSSue_oon: 37 $\mspace{11mu}{{d_{u}(n)} = \left\{ \begin{matrix}e^{{- j}\frac{\pi\;{{un}{({n + 1})}}}{63}} & {{n = 0},1,\ldots\mspace{14mu},30} \\e^{{- j}\frac{\pi\;{u{({n + 1})}}{({n + 2})}}{63}} & {{n = 31},32,\ldots\mspace{14mu},61}\end{matrix} \right.}$ SSSS  Sequence${d\left( {2\; n} \right)} = \left\{ {{\begin{matrix}{{s_{0}^{(m_{0})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu}{subframe}\mspace{14mu} 0} \\{{s_{1}^{(m_{1})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu}{subframe}\mspace{14mu} 5}\end{matrix}{d\left( {{2\; n} + 1} \right)}} = \left\{ {{{\begin{matrix}{{s_{1}^{(m_{1})}(n)}{c_{1}(n)}{z_{1}^{(m_{0})}(n)}} & {{in}\mspace{14mu}{subframe}\mspace{14mu} 0} \\{{s_{0}^{(m_{0})}(n)}{c_{1}(n)}{z_{1}^{(m_{1})}(n)}} & {{in}\mspace{14mu}{subframe}\mspace{14mu} 5}\end{matrix}m_{0}} = {{m^{\prime}\;{mod}\; 31m_{1}} = {{\left( {m_{0} + \left\lfloor {m^{\prime}/31} \right\rfloor + 1} \right){mod}\; 31m^{\prime}} = {N_{ID}^{(1)} + {{q\left( {q + 1} \right)}/2}}}}},{q = \left\lfloor \frac{N_{ID}^{(1)} + {{q^{\prime}\left( {q^{\prime} + 1} \right)}/2}}{30} \right\rfloor},{q^{\prime} = {{\left\lfloor {N_{ID}^{(1)}/30} \right\rfloor{c_{0}(n)}} = {{{\overset{\sim}{c}\left( {\left( {n + N_{ID}^{(2)}} \right){mod}\; 31} \right)}{c_{1}(n)}} = {\overset{\sim}{c}\left( {\left( {n + N_{ID}^{(2)} + 3} \right){mod}\; 31} \right)}}}}} \right.} \right.$—Utilization of Origin Information—

The selection unit 240 of the UE 20 selects a synchronization signal byusing the origin information. Hereinafter, a specific example of theselection of a synchronization signal using origin information will bedescribed.

1)

The following are examples of synchronization signals that the UE 20 mayreceive. Note that the number of hops indicated below corresponds to thenumber of interposing devices in the relaying procedure.

A. Source device=GPS satellite, number of hops=0 (direct reception fromGPS satellite)

B. Source device=eNB, number of hops=0 (direct reception from eNB)

C. Transmitting device=RSU

C-1. Source device=GPS satellite, number of hops=1

C-2. Source device=eNB, number of hops=1

C-3. Source device=RSU, number of hops=1

C-4. Source device=UE, number of hops=1

C-5. Source device=transmitting device, number of hops=0

D. Transmitting device=UE

D-1. Source device=GPS satellite, number of hops=1

D-2. Source device=eNB, number of hops=1

D-3. Source device=RSU, number of hops=1

D-4. Source device=UE, number of hops=1

D-5. Source device=transmitting device, number of hops=0

For example, the selection unit 240 may select with the highest prioritya synchronization signal for which the type of source device is the GPSsatellite 40, and select with the next-highest priority asynchronization signal for which the type of source device is the eNB30. Specifically, the selection unit 240 may select a synchronizationsignal according to the following priority ranking 1.

Priority ranking1=(A)>(B)>(C-1)>(D-1)>(C-2)>(D-2)>(C-3)>(D-3)>(C-4)>(D-4)>(C-5)>(D-5)

Alternatively, the selection unit 240 may prioritize the selection of asynchronization signal with a low number of hops. Specifically, theselection unit 240 may select a synchronization signal according toeither of the following priority rankings.

Priority ranking2=(A)>(B)>(C-5)>(D-5)>(C-1)>(D-1)>(C-2)>(D-2)>(C-3)>(D-3)>(C-4)>(D-4)

Priority ranking3=(A)>(B)>(C-5)>(D-5)>(C-1)>(C-2)>(D-1)>(D-2)>(C-3)>(D-3)>(C-4)>(D-4)

2)

As another example, if the origin information is expressed in a bit mapformat, the selection unit 240 of the UE 20 may compute a quality scorefrom the bit map, and select the synchronization signal with the highestscore. For example, the selection unit 240 may compute a score accordingto the following Formula 1.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{\sum\limits_{n = 0}^{{Total}\mspace{14mu}{hops}}{\left( \frac{n + 1}{{{Total}\mspace{14mu}{hops}} + 1} \right)\left( {{Node}\mspace{14mu}{score}\mspace{14mu} n} \right)}} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

According to Formula 1 above, in a case in which synchronization timingsare relayed in the order of GPS satellite→eNB→RSU→UE, the node score ofthe GPS satellite is “4”, the node score of the eNB is “3”, the nodescore of the RSU is “2”, and the node score of the UE is “1”, the scorebecomes “4.33” according to the calculation (1/3)*4+(2/3)*3+(3/3)*2. Thescore calculation method according to Formula 1 may be considered to bea method that places importance on the types of downstream devices inthe relaying procedure.

On the other hand, the selection unit 240 may also use a scorecalculation method that places importance on the types of upstreamdevices in the relaying procedure. Such a calculation method isexpressed like in the following Formula 2, for example.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack & \; \\{\sum\limits_{n = 0}^{{Total}\mspace{14mu}{hops}}{\left( \frac{{{Total}\mspace{14mu}{hops}} + 1 - n}{{{Total}\mspace{14mu}{hops}} + 1} \right)\left( {{Node}\mspace{14mu}{score}\mspace{14mu} n} \right)}} & \left( {{Formula}\mspace{14mu} 2} \right)\end{matrix}$

According to Formula 2 above, in a case in which synchronization timingsare relayed in the order of GPS satellite→eNB→RSU→UE, the node score ofthe GPS satellite is “4”, the node score of the eNB is “3”, the nodescore of the RSU is “2”, and the node score of the UE is “1”, the scorebecomes “6.67” according to the calculation (3/3)*4+(2/3)*3+(1/3)*2.

Note that the communication device that transmits a synchronizationsignal may also transmit, as the origin information, a score computed bya calculation method described with reference to Formula 1 and Formula 2or the like. In a case of calculating the score on the side of thereceiving UE 20, the same score calculation is performed on multiple UEs20 for one transmitting communication device. On the other hand, in thecase in which the transmitting communication device calculates andtransmits the score, it is sufficient to perform the score calculationon only one communication device (namely, the transmitting communicationdevice). Consequently, by having the transmitting communication devicecalculate and transmit the score, it is possible to moderate the load onthe wireless communication system overall.

Additionally, the above score may also be used in the quality thresholdvalue determination described with reference to S512.

In addition, the control unit 260 may also determine whether or not totransmit a synchronization signal after synchronization timings areacquired by the synchronization process, based on the origin informationof the synchronization signal selected by the selection unit 240. Forexample, since the degradation of accuracy is a concern for asynchronization signal with a large number of hops, the control unit 260may determine not to transmit a synchronization signal if the number ofhops exceeds a threshold value. According to such a configuration, theprolonged propagation of a synchronization signal with degraded accuracywithin the wireless communication system may be prevented.

—Application Example—

Next, an application example of the second operation example discussedabove will be described. The present application example is a technologydevised primarily by supposing a situation in which the synchronizedstates of multiple UEs 20 moving along the same route are lost aroundthe same time. For example, if multiple UEs 20 synchronized to asynchronization signal transmitted from the GPS satellite 40 enter atunnel around the same time, the synchronized states of the multiple UEs20 may be lost around the same time. This point will be described withreference to FIG. 11.

FIG. 11 is an explanatory diagram illustrating an operation example in acase in which the synchronized states of multiple UEs 20 are lost aroundthe same time. In a case in which the UEs 20A to 20C are synchronized toa synchronization signal transmitted from the same GPS satellite 40, asillustrated in FIG. 11, the UEs 20A to 20C operate in accordance withthe same synchronization timings. Subsequently, if at time t1 the UEs20A to 20C enter a tunnel and the synchronized states of the UEs 20A to20C are lost, each of the UEs 20A to 20C may attempt to transmit asynchronization signal in accordance with the process of S510illustrated in FIG. 10.

Herein, synchronization signal resources are mapped periodically (forexample, on a 40 ms period) inside the frame, as illustrated in FIG. 11.For this reason, if the synchronized states of the UEs 20A to 20C arelost at time t1, the UEs 20A to 20C may conduct the transmission of asynchronization signal in the same synchronization signal resourcearriving next at time t2.

However, if the UEs 20A to 20C transmit synchronization signals at thesame time t2, each of the UEs 20A to 20C will have difficulty receivingthe synchronization signals transmitted from the other UEs 20 among theUEs 20A to 20C.

Accordingly, in a case where the synchronized states of multiple UEs 20are lost around the same time, the UE 20 according to the applicationexample conducts the transmission of a synchronization signal at adifferent timing from other UEs 20. For example, as illustrated in FIG.12, after time t1 in a case where the synchronized states of multipleUEs 20 are lost around the same time, the UE 20 according to theapplication example attempts to transmit a synchronization signal at adifferent timing. However, if the UE 20B transmits a synchronizationsignal first as illustrated in FIG. 12, the UEs 20A and 20C receive thesynchronization signal, and thus, as illustrated in FIG. 13, the UEs 20Aand 20C do not transmit synchronization signals, and instead synchronizeto the synchronization signal transmitted by the UE 20B. According tosuch a configuration, in a case where the synchronized states ofmultiple UEs 20 based on a synchronization signal from the GPS satellite40 or the eNB 30 are lost around the same time, it is possible to switchsmoothly to synchronization and D2D communication among the UEs 20.

Note that the above timing control may be realized by various methods.For example, in a case where the synchronized state is lost, the controlunit 260 may generate a random number, and control the transmission of asynchronization signal at a timing corresponding to the generated randomnumber. In addition, the control unit 260 may also generate a randomnumber for determining whether or not to transmit a synchronizationsignal in each synchronization signal resource, and transmit asynchronization signal in the synchronization signal resourcecorresponding to a case in which the random number satisfies a certaincondition.

Additionally, the control unit 260 may also control the transmission ofa synchronization signal at a timing corresponding to informationincluded in the UE 20. For example, the UE 20 may decide the timing atwhich to transmit a synchronization signal according to(synchronization_signal_resource_number mod IMSI or RNTI).Alternatively, another communication device such as the eNB 30 or theRSU 50 may designate in advance the UE 20 to transmit a synchronizationsignal, and the designated UE 20 may transmit the synchronizationsignal. Note that another communication device such as the eNB 30 or theRSU 50 may also designate in advance to each UE 20 a timing at which totransmit a synchronization signal, and each UE 20 may wait until thedesignated timing before transmitting a synchronization signal.

3-3. Third Operation Example

The above thus describes a second operation example according to anembodiment of the present disclosure. Next, a third operation exampleaccording to an embodiment of the present disclosure will be described.The third operation example is a technology that enables the UE 20 tosynchronize based on a GNSS signal transmitted from the GPS satellite40, while also reducing power consumption in the UE 20.

—Introduction—

Since there are battery concerns about the UE 20, it is anticipated thatthe GNSS signal processing unit 220 will be activated and deactivatedrepeatedly. For this reason, it is difficult for the UE 20 tocontinually maintain synchronization based on a GNSS signal transmittedfrom the GPS satellite 40. On the other hand, even if the UE 20 isunable to receive a GNSS signal transmitted from the GPS satellite 40,the UE 20 is still able to share synchronization timings with the eNB 30based on a synchronization signal from the eNB 30.

However, if a UE 20 with an active GNSS signal processing unit 220conducts the synchronization process based on the GNSS signal, and a UE20 with an inactive GNSS signal processing unit 220 conducts thesynchronization process based on a synchronization signal transmittedfrom the eNB 30, there will be a mixture of UEs 20 synchronized todifferent types of source devices. From the perspective of networkoperation and management, it is desirable for the type of source deviceto which each UE 20 synchronizes to be unified to some degree.

The third operation example is a technology devised in light of theabove circumstances. According to the third operation example, even a UE20 with an inactive GNSS signal processing unit 220 is able to obtainsynchronization timings according to a GNSS signal transmitted from theGPS satellite 40. Hereinafter, a method of realizing such a thirdoperation example will be described specifically.

—Main Issue—

In the third operation example, the eNB 30 or the RSU 50 transmits anoffset value indicating the time different between a synchronizationtiming obtained using the synchronization signal transmitted by the eNB30 or the RSU 50, and a synchronization timing acquired based on a GNSSsignal. At this point, a specific example of an offset value will bedescribed with reference to FIG. 14.

FIG. 14 is an explanatory diagram illustrating a specific example of anoffset value. As illustrated in FIG. 14, a synchronization timingobtained using a synchronization signal transmitted by the eNB 30 and asynchronization timing obtained using a GNSS signal arrive periodically.Herein, if the periods of both synchronization timings are the same, thetime difference between both of the synchronization timings is alsoconstant. Accordingly, in the present operation example, the eNB 30 orthe RSU 50 transmits the time difference between both of thesynchronization timings to the UE 20 as an offset value.

Subsequently, from the synchronization timing obtained using asynchronization signal transmitted by the eNB 30 or the RSU 50, thesynchronization processing unit 250 of the UE 20 specifies, as thesynchronization timing, a timing that has been time-shifted according tothe above offset value. According to such a configuration, even whilethe GNSS signal processing unit 220 is inactive in the UE 20, the UE 20still is able to obtain a synchronization timing obtained using the GNSSsignal. As a result, it is possible to improve a mixed state of UEs 20synchronized to different types of source devices.

Note that the eNB 30 or the RSU 50 may acquire the offset value by avariety of methods. Hereinafter, offset value acquisition methods willbe described with reference to FIG. 15.

FIG. 15 is an explanatory diagram illustrating several methods by whichthe eNB 30 or the RSU 50 acquires an offset value.

(a)

For example, if the serving eNB 30 or RSU 50 includes a GNSS signalprocessing unit, the serving eNB 30 or RSU 50 receives a GNSS signal toacquire a synchronization timing, and calculates the time differencebetween the acquired synchronization timing and its own synchronizationtiming as an offset value (S604). Subsequently, the serving eNB 30 orRSU 50 transmits the above offset value to the UE 20 (S608).

(b)

On the other hand, cases in which the serving eNB 30 or RSU 50 does notinclude a GNSS signal processing unit are also conceivable. In suchcases, the serving eNB 30 or RSU 50 may acquire the offset value bycooperating with another communication device.

(b-1)

For example, the serving eNB 30 or RSU 50 may request an offset valuefrom another eNB 32 that includes a GNSS signal processing unit (S612),and the other eNB 32 may calculate the offset value (S616).Subsequently, the serving eNB 30 or RSU 50 receives the offset valuefrom the other eNB 32 (S620), and transmits the offset value to the UE20 (S624).

However, in the case in which the serving eNB 30 or RSU 50 and the othereNB 32 are not synchronized, if the serving eNB 30 or RSU 50 simplytransmits the offset value received from the other eNB 32 directly, acorrect synchronization timing will not be obtained in the UE 20.Accordingly, in the case in which the serving eNB 30 or RSU 50 and theother eNB 32 are not synchronized, the serving eNB 30 or RSU 50 mayrecalculate the offset value by adding together the offset valuereceived from the other eNB 32 and the synchronization shift from theother eNB 32. Alternatively, the eNB 32 may request an offset value fromthe network (S628), receive an offset value calculated on the network(S632, S636), and transmit this offset value to the UE 20 (S644).

(b-2)

As another method, the serving eNB 30 or RSU 50 may also acquire anoffset value calculated by a vehicle 22 or a UE 20 including thefunction of a GNSS signal processing unit. For example, the serving eNB30 may request the calculation of an offset value from a vehicle 22including the function of a GNSS signal processing unit (S648, S652),receive the offset value calculated by the vehicle 22 from the vehicle22 (S656, S660), and transmit the offset value to the UE 20 (S664).

Note that the serving eNB 30 may request the calculation of an offsetvalue only from a specific communication device from among communicationdevices such as the UE 20 or the vehicle 22, or request the calculationof an offset value from all communication devices. If offset values arereceived from multiple communication devices as a result, the servingeNB 30 may also calculate the average of the multiple offset values asthe offset value to report to the UE 20. Alternatively, the serving eNB30 may store the position information and the offset value of eachcommunication device in association with each other. In this case, theserving eNB 30 may set a different offset value for each area. Forexample, the serving eNB 30 may unicast or multicast the offset valuecalculated by a communication device belonging to each area to UEs 20within the corresponding area. Since the offset value is expected to bedifferent depending on the position of the UE 20, with the aboveconfiguration, the UE 20 becomes able to specify more accurately asynchronization timing based on a GNSS signal.

Alternatively, if the serving eNB 30 performs the transmission of anoffset value in a certain field of a frame (such as the MIB or the SIB,for example), a UE 20 including the function of the GNSS signalprocessing unit 220 may also determine whether or not to perform thecalculation of an offset value based on whether or not an offset valueis set in the certain field.

For example, if an offset value is not set in the certain field, thecontrol unit 260 of the UE 20 may control the calculation and thetransmission of an offset value. Alternatively, if an offset value isnot set in the certain field, the control unit 260 of the UE 20 maycontrol whether or not to perform the calculation and the transmissionof an offset value randomly, based on probability information designatedin advance from the eNB 30, for example. According to such aconfiguration, if an offset value is not set in the certain field, it ispossible to avoid a situation in which all UEs 20 including the functionof the GNSS signal processing unit 220 perform the calculation and thetransmission of an offset value.

Note that the eNB 30 may also set the above probability informationbased on the number of UEs 20 belonging to the cell. For example, theeNB 30 may set the above probability information so that the offsetvalue transmission probability decreases as the number of UEs 20belonging to the cell increases. According to such a configuration, theeNB 30 is able to obtain a number of offset values close to a certainnumber, irrespective of the number of UEs 20 belonging to the cell.

Alternatively, the eNB 30 may also use the SIB or the DCI, for example,to designate in advance the UE 20 to perform the calculation and thetransmission of an offset value.

—Supplemental Remarks—

The above supposes a situation in which the UE 20 is able to receive asynchronization signal transmitted by the eNB 30 or the RSU 50. However,situations in which the UE 20 is unable to receive a synchronizationsignal transmitted by the eNB 30 or the RSU 50 are also anticipated. Inthis way, if the UE 20 becomes unable to receive a synchronizationsignal transmitted by the eNB 30 or the RSU 50, the UE 20 may alsoforcibly activate the GNSS signal processing unit 220. Alternatively, torealize the seamless handover of a synchronization signal, if the UE 20seems likely to become unable to receive a synchronization signaltransmitted by the eNB 30 or the RSU 50, such as if the received signalstrength falls below a threshold value, for example, the UE 20 mayforcibly activate the GNSS signal processing unit 220. Since situationsin which the UE 20 is unable to receive a synchronization signaltransmitted from the eNB 30 or the RSU 50 are not major in terms ofoverall usage situations, the above configuration does not pose aproblem from the perspective of power consumption.

4. APPLICATION EXAMPLES

The technology of the present disclosure is applicable to variousproducts. For example, the eNB 30 described above is an example of abase station, and the base station may be realized as any type ofevolved Node B (eNB) such as a macro eNB, and a small eNB. A small eNBmay be an eNB that covers a cell smaller than a macro cell, such as apico eNB, micro eNB, or home (femto) eNB. Instead, the base station maybe realized as any other types of base stations such as a NodeB and abase transceiver station (BTS). The base station may include a main body(that is also referred to as a base station device) configured tocontrol radio communication, and one or more remote radio heads (RRH)disposed in a different place from the main body. Additionally, varioustypes of terminals to be discussed later may also operate as the basestation by temporarily or semi-permanently executing a base stationfunction.

For example, the UE 20 may be realized as a mobile terminal such as asmartphone, a tablet personal computer (PC), a notebook PC, a portablegame terminal, a portable/dongle type mobile router, and a digitalcamera, or an in-vehicle terminal such as a car navigation device. TheUE 20 may also be realized as a terminal (that is also referred to as amachine type communication (MTC) terminal) that performsmachine-to-machine (M2M) communication. Furthermore, the UE 20 may be aradio communication module (such as an integrated circuit moduleincluding a single die) mounted on each of the terminals.

4-1. Application Examples Regarding Base Station First ApplicationExample

FIG. 16 is a block diagram illustrating a first example of a schematicconfiguration of an eNB to which the technology of the presentdisclosure may be applied. An eNB 800 includes one or more antennas 810and a base station device 820. Each antenna 810 and the base stationdevice 820 may be connected to each other via an RF cable.

Each of the antennas 810 includes a single or multiple antenna elements(such as multiple antenna elements included in an MIMO antenna), and isused for the base station device 820 to transmit and receive radiosignals. The eNB 800 may include the multiple antennas 810, asillustrated in FIG. 16. For example, the multiple antennas 810 may becompatible with multiple frequency bands used by the eNB 800. Note thatalthough FIG. 16 illustrates the example in which the eNB 800 includesthe multiple antennas 810, the eNB 800 may also include a single antenna810.

The base station device 820 includes a controller 821, a memory 822, anetwork interface 823, and a radio communication interface 825.

The controller 821 may be, for example, a CPU or a DSP, and operatesvarious functions of a higher layer of the base station device 820. Forexample, the controller 821 generates a data packet from data in signalsprocessed by the radio communication interface 825, and transfers thegenerated packet via the network interface 823. The controller 821 maybundle data from multiple base band processors to generate the bundledpacket, and transfer the generated bundled packet. In addition, thecontroller 821 may have logical functions of performing control such asradio resource control, radio bearer control, mobility management,admission control, and scheduling. In addition, the control may beperformed in corporation with an eNB or a core network node in thevicinity. The memory 822 includes RAM and ROM, and stores a program thatis executed by the controller 821, and various types of control data(such as a terminal list, transmission power data, and scheduling data).

The network interface 823 is a communication interface for connectingthe base station device 820 to a core network 824. The controller 821may communicate with a core network node or another eNB via the networkinterface 823. In that case, the eNB 800, and the core network node orthe other eNB may be connected to each other through a logical interface(such as an Si interface and an X2 interface). The network interface 823may also be a wired communication interface or a radio communicationinterface for radio backhaul. If the network interface 823 is a radiocommunication interface, the network interface 823 may use a higherfrequency band for radio communication than a frequency band used by theradio communication interface 825.

The radio communication interface 825 supports any cellularcommunication scheme such as Long Term Evolution (LTE) and LTE-Advanced,and provides radio connection to a terminal positioned in a cell of theeNB 800 via the antenna 810. The radio communication interface 825 maytypically include, for example, a baseband (BB) processor 826 and an RFcircuit 827. The BB processor 826 may perform, for example,encoding/decoding, modulating/demodulating, andmultiplexing/demultiplexing, and performs various types of signalprocessing of layers (such as L1, medium access control (MAC), radiolink control (RLC), and a packet data convergence protocol (PDCP) forexample). The BB processor 826 may have a part or all of theabove-described logical functions instead of the controller 821. The BBprocessor 826 may be a memory that stores a communication controlprogram, or a module that includes a processor and a related circuitconfigured to execute the program. Updating the above program may allowthe functions of the BB processor 826 to be changed. The above modulemay be a card or a blade that is inserted into a slot of the basestation device 820. Alternatively, the module may also be a chip that ismounted on the above card or the above blade. Meanwhile, the RF circuit827 may include, for example, a mixer, a filter, an amplifier, and thelike and transmits and receives radio signals via the antenna 810.

The radio communication interface 825 may include the multiple BBprocessors 826, as illustrated in FIG. 16. For example, the multiple BBprocessors 826 may be compatible with multiple frequency bands used bythe eNB 800. In addition, the radio communication interface 825 mayinclude the multiple RF circuits 827, as illustrated in FIG. 16. Forexample, the multiple RF circuits 827 may be compatible with multipleantenna elements. Note that although FIG. 16 illustrates the example inwhich the radio communication interface 825 includes the multiple BBprocessors 826 and the multiple RF circuits 827, the radio communicationinterface 825 may also include a single BB processor 826 or a single RFcircuit 827.

Second Application Example

FIG. 17 is a block diagram illustrating a second example of a schematicconfiguration of an eNB to which the technology of the presentdisclosure may be applied. An eNB 830 includes one or more antennas 840,a base station device 850, and an RRH 860. Each antenna 840 and the RRH860 may be connected to each other via an RF cable. In addition, thebase station device 850 and the RRH 860 may be connected to each othervia a high speed line such as an optical fiber cable.

Each of the antennas 840 includes a single or multiple antenna elements(such as multiple antenna elements included in an MIMO antenna), and isused for the RRH 860 to transmit and receive radio signals. The eNB 830may include the multiple antennas 840, as illustrated in FIG. 17. Forexample, the multiple antennas 840 may be compatible with multiplefrequency bands used by the eNB 830. Note that although FIG. 17illustrates the example in which the eNB 830 includes the multipleantennas 840, the eNB 830 may also include a single antenna 840.

The base station device 850 includes a controller 851, a memory 852, anetwork interface 853, a radio communication interface 855, and aconnection interface 857. The controller 851, the memory 852, and thenetwork interface 853 are the same as the controller 821, the memory822, and the network interface 823 described with reference to FIG. 16.

The radio communication interface 855 supports any cellularcommunication scheme such as LTE and LTE-Advanced, and provides radiocommunication to a terminal positioned in a sector corresponding to theRRH 860 via the RRH 860 and the antenna 840. The radio communicationinterface 855 may typically include, for example, a BB processor 856 orthe like. The BB processor 856 is the same as the BB processor 826described with reference to FIG. 16, except the BB processor 856 isconnected to the RF circuit 864 of the RRH 860 via the connectioninterface 857. The radio communication interface 855 may include themultiple BB processors 856, as illustrated in FIG. 17. For example, themultiple BB processors 856 may be compatible with multiple frequencybands used by the eNB 830. Note that although FIG. 17 illustrates theexample in which the radio communication interface 855 includes themultiple BB processors 856, the radio communication interface 855 mayalso include a single BB processor 856.

The connection interface 857 is an interface for connecting the basestation device 850 (radio communication interface 855) to the RRH 860.The connection interface 857 may also be a communication module forcommunication in the above-described high speed line that connects thebase station device 850 (radio communication interface 855) to the RRH860.

In addition, the RRH 860 includes a connection interface 861 and a radiocommunication interface 863.

The connection interface 861 is an interface for connecting the RRH 860(radio communication interface 863) to the base station device 850. Theconnection interface 861 may also be a communication module forcommunication in the above-described high speed line.

The radio communication interface 863 transmits and receives radiosignals via the antenna 840. The radio communication interface 863 maytypically include, for example, the RF circuit 864 or the like. The RFcircuit 864 may include, for example, a mixer, a filter, an amplifier,and the like, and transmits and receives radio signals via the antenna840. The radio communication interface 863 may include multiple RFcircuits 864, as illustrated in FIG. 17. For example, the multiple RFcircuits 864 may support multiple antenna elements. Note that althoughFIG. 17 illustrates the example in which the radio communicationinterface 863 includes the multiple RF circuits 864, the radiocommunication interface 863 may also include a single RF circuit 864.

In the eNB 800 and the eNB 830 illustrated in FIGS. 16 and 17, thecommunication unit 310 described using FIG. 5 may be implemented in theradio communication interface 825 as well as the radio communicationinterface 855 and/or the radio communication interface 863. Also, atleast some of these functions may also be implemented in the controller821 and the controller 851.

4-2. Application Examples Regarding UE First Application Example

FIG. 18 is a block diagram illustrating an example of a schematicconfiguration of a smartphone 900 that is an example of the UE 30 towhich the technology of the present disclosure may be applied. Thesmartphone 900 includes a processor 901, a memory 902, a storage 903, anexternal connection interface 904, a camera 906, a sensor 907, amicrophone 908, an input device 909, a display device 910, a speaker911, a radio communication interface 912, one or more antenna switches915, one or more antennas 916, a bus 917, a battery 918, and anauxiliary controller 919.

The processor 901 may be, for example, a CPU or a system on a chip(SoC), and controls functions of an application layer and another layerof the smartphone 900. The memory 902 includes RAM and ROM, and stores aprogram that is executed by the processor 901, and data. The storage 903may include a storage medium such as a semiconductor memory and a harddisk. The external connection interface 904 is an interface forconnecting an external device such as a memory card and a universalserial bus (USB) device to the smartphone 900.

The camera 906 includes an image sensor such as a charge coupled device(CCD) and a complementary metal oxide semiconductor (CMOS), andgenerates a captured image. The sensor 907 may include a group ofsensors such as a measurement sensor, a gyro sensor, a geomagneticsensor, and an acceleration sensor. The microphone 908 converts soundsthat are input to the smartphone 900 to audio signals. The input device909 includes, for example, a touch sensor configured to detect touchonto a screen of the display device 910, a keypad, a keyboard, a button,a switch, or the like, and receives an operation or an information inputfrom a user. The display device 910 includes a screen such as a liquidcrystal display (LCD) and an organic light-emitting diode (OLED)display, and displays an output image of the smartphone 900. The speaker911 converts audio signals that are output from the smartphone 900 tosounds.

The radio communication interface 912 supports any cellularcommunication scheme such as LTE and LTE-Advanced, and performs radiocommunication. The radio communication interface 912 may typicallyinclude, for example, a BB processor 913, an RF circuit 914, and thelike. The BB processor 913 may perform, for example, encoding/decoding,modulating/demodulating, multiplexing/demultiplexing, and the like, andperforms various types of signal processing for radio communication.Meanwhile, the RF circuit 914 may include, for example, a mixer, afilter, an amplifier, and the like, and transmits and receives radiosignals via the antenna 916. The radio communication interface 912 mayalso be a one chip module that has the BB processor 913 and the RFcircuit 914 integrated thereon. The radio communication interface 912may include the multiple BB processors 913 and the multiple RF circuits914, as illustrated in FIG. 18. Note that although FIG. 18 illustratesthe example in which the radio communication interface 912 includes themultiple BB processors 913 and the multiple RF circuits 914, the radiocommunication interface 912 may also include a single BB processor 913or a single RF circuit 914.

Furthermore, in addition to a cellular communication scheme, the radiocommunication interface 912 may support another type of radiocommunication scheme such as a short-distance wireless communicationscheme, a near field communication scheme, and a radio local areanetwork (LAN) scheme. In that case, the radio communication interface912 may include the BB processor 913 and the RF circuit 914 for eachradio communication scheme.

Each of the antenna switches 915 switches connection destinations of theantennas 916 among multiple circuits (such as circuits for differentradio communication schemes) included in the radio communicationinterface 912.

Each of the antennas 916 includes a single or multiple antenna elements(such as multiple antenna elements included in an MIMO antenna), and isused for the radio communication interface 912 to transmit and receiveradio signals. The smartphone 900 may include the multiple antennas 916,as illustrated in FIG. 18. Note that although FIG. 18 illustrates theexample in which the smartphone 900 includes the multiple antennas 916,the smartphone 900 may also include a single antenna 916.

Furthermore, the smartphone 900 may include the antenna 916 for eachradio communication scheme. In that case, the antenna switches 915 maybe omitted from the configuration of the smartphone 900.

The bus 917 connects the processor 901, the memory 902, the storage 903,the external connection interface 904, the camera 906, the sensor 907,the microphone 908, the input device 909, the display device 910, thespeaker 911, the radio communication interface 912, and the auxiliarycontroller 919 to each other. The battery 918 supplies power to blocksof the smartphone 900 illustrated in FIG. 18 via feeder lines, which arepartially shown as dashed lines in the figure. The auxiliary controller919 operates a minimum necessary function of the smartphone 900, forexample, in a sleep mode.

In the smartphone 900 illustrated in FIG. 18, the communication unit 210described using FIG. 5 may be implemented in the radio communicationinterface 912. Also, at least some of these functions may also beimplemented in the processor 901 or the auxiliary controller 919.

Second Application Example

FIG. 19 is a block diagram illustrating an example of a schematicconfiguration of a car navigation device 920 to which the technology ofthe present disclosure may be applied. The car navigation device 920includes a processor 921, a memory 922, a global positioning system(GPS) module 924, a sensor 925, a data interface 926, a content player927, a storage medium interface 928, an input device 929, a displaydevice 930, a speaker 931, a radio communication interface 933, one ormore antenna switches 936, one or more antennas 937, and a battery 938.

The processor 921 may be, for example, a CPU or a SoC, and controls anavigation function and another function of the car navigation device920. The memory 922 includes RAM and ROM, and stores a program that isexecuted by the processor 921, and data.

The GPS module 924 uses GPS signals received from a GPS satellite tomeasure a position (such as latitude, longitude, and altitude) of thecar navigation device 920. The sensor 925 may include a group of sensorssuch as a gyro sensor, a geomagnetic sensor, and a barometric sensor.The data interface 926 is connected to, for example, an in-vehiclenetwork 941 via a terminal that is not shown, and acquires datagenerated by the vehicle, such as vehicle speed data.

The content player 927 reproduces content stored in a storage medium(such as a CD and a DVD) that is inserted into the storage mediuminterface 928. The input device 929 includes, for example, a touchsensor configured to detect touch onto a screen of the display device930, a button, or a switch, and receives an operation or an informationinput from a user. The display device 930 includes a screen such as aLCD or an OLED display, and displays an image of the navigation functionor content that is reproduced. The speaker 931 outputs sounds of thenavigation function or the content that is reproduced.

The radio communication interface 933 supports any cellularcommunication scheme such as LET and LTE-Advanced, and performs radiocommunication. The radio communication interface 933 may typicallyinclude, for example, a BB processor 934, an RF circuit 935, and thelike. The BB processor 934 may perform, for example, encoding/decoding,modulating/demodulating, multiplexing/demultiplexing, and the like, andperforms various types of signal processing for radio communication.Meanwhile, the RF circuit 935 may include, for example, a mixer, afilter, an amplifier, and the like, and transmits and receives radiosignals via the antenna 937. The radio communication interface 933 maybe a one chip module having the BB processor 934 and the RF circuit 935integrated thereon. The radio communication interface 933 may includethe multiple BB processors 934 and the multiple RF circuits 935, asillustrated in FIG. 19. Note that although FIG. 19 illustrates theexample in which the radio communication interface 933 includes themultiple BB processors 934 and the multiple RF circuits 935, the radiocommunication interface 933 may also include a single BB processor 934or a single RF circuit 935.

Furthermore, in addition to a cellular communication scheme, the radiocommunication interface 933 may support another type of radiocommunication scheme such as a short-distance wireless communicationscheme, a near field communication scheme, and a radio LAN scheme. Inthat case, the radio communication interface 933 may include the BBprocessor 934 and the RF circuit 935 for each radio communicationscheme.

Each of the antenna switches 936 switches connection destinations of theantennas 937 among multiple circuits (such as circuits for differentradio communication schemes) included in the radio communicationinterface 933.

Each of the antennas 937 includes a single or multiple antenna elements(such as multiple antenna elements included in an MIMO antenna), and isused for the radio communication interface 933 to transmit and receiveradio signals. The car navigation device 920 may include the multipleantennas 937, as illustrated in FIG. 19. Note that although FIG. 19illustrates the example in which the car navigation device 920 includesthe multiple antennas 937, the car navigation device 920 may alsoinclude a single antenna 937.

Furthermore, the car navigation device 920 may include the antenna 937for each radio communication scheme. In that case, the antenna switches936 may be omitted from the configuration of the car navigation device920.

The battery 938 supplies power to each block of the car navigationdevice 920 illustrated in FIG. 19 via feeder lines that are partiallyshown as dashed lines in the figure. In addition, the battery 938accumulates power supplied form the vehicle.

In the car navigation device 920 illustrated in FIG. 19, thecommunication unit 210 described using FIG. 5 may be implemented in theradio communication interface 933. Also, at least some of thesefunctions may also be implemented in the processor 921.

In addition, the technology of the present disclosure may also berealized as an in-vehicle system (or a vehicle) 940 including one ormore blocks of the above car navigation device 920, the in-vehiclenetwork 941, and a vehicle module 942. The vehicle module 942 generatesvehicle data such as vehicle speed, engine speed, and troubleinformation, and outputs the generated data to the in-vehicle network941.

5. CONCLUSION

As described above, according to the first operation example and thesecond operation example of the present disclosure, the UE 20 is able toselect a synchronization signal appropriately and conduct asynchronization process. In addition, according to the third operationexample of the present disclosure, it is possible to synchronize the UE20 based on a GNSS signal transmitted from the GPS satellite 40, whilealso reducing power consumption in the UE 20.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

For example, the respective steps in the processes of the UE 20 and theeNB 30 in this specification are not strictly limited to being processedin a time series following the order described as sequence diagramsherein. For example, the respective steps in the processes of the UE 20and the eNB 30 may be processed in an order that differs from the orderdescribed as sequence diagrams herein, and furthermore may be processedin parallel.

Also, it is possible to create a computer program for causing hardwaresuch as the CPU, ROM, and RAM built into the above UE 20 and the eNB 30to exhibit the same functionality as the respective components of the UE20 and the eNB 30 discussed earlier. Also, a storage medium having sucha computer program stored therein is also provided.

In addition, the advantageous effects described in this specificationare merely for the sake of explanation or illustration, and are notlimiting. In other words, instead of or in addition to the aboveadvantageous effects, technology according to an embodiment of thepresent disclosure may exhibit other advantageous effects that are clearto persons skilled in the art from the description of thisspecification. For example, a communication device simultaneouslyimplementing the functions from the first operation example to the thirdoperation example discussed earlier may also be provided.

Additionally, the present technology may also be configured as below.

(1)

A communication device including:

a selection unit configured to select a synchronization signal fromrespective synchronization signals received from two or more otherdevices on a basis of origin information that is acquired bycommunication with another device and that indicates an origin of asynchronization signal used for acquisition of synchronization timing

in the other device; and a synchronization processing unit configured toacquire synchronization timing using the synchronization signal selectedby the selection unit.

(2)

The communication device according to (1), in which

the origin information includes information corresponding to a sourcedevice serving as a source of a synchronization signal for theacquisition of the synchronization timing in the other device.

(3)

The communication device according to (2), in which

the origin information includes information that indicates a procedureof relaying the synchronization timing from the source device to theother device.

(4)

The communication device according to (3), in which

the origin information includes number-of-interpositions informationthat indicates a number of interposing devices in the procedure ofrelaying the synchronization timing from the source device to the otherdevice.

(5)

The communication device according to any one of (2) to (4), in which

the selection unit recognizes a source device corresponding to asynchronization signal received from the other device on a basis of theorigin information, and prioritize, among a synchronization signalcorresponding to a first source device and a synchronization signalcorresponding to a second source device according to a system thatprovides service in a wider range compared with the first source device,selection of the synchronization signal corresponding to the secondsource device.

(6)

The communication device according to (5), in which

the first source device is a cellular base station, and the secondsource device is a GPS satellite.

(7)

The communication device according to (4), in which

the selection unit recognizes a number of interposing devices in arelaying procedure corresponding to a synchronization signal receivedfrom the other device on a basis of the number-of-interpositionsinformation, and prioritize, among a synchronization signalcorresponding to a first relaying procedure and a synchronization signalcorresponding to a second relay procedure having a larger number ofinterposing devices compared with the first relaying procedure,selection of the synchronization signal corresponding to the firstrelaying procedure.

(8)

The communication device according to (1), in which

the origin information includes score information calculated on a basisof the origin of the synchronization signal used for acquisition of thesynchronization timing in the other device, and

the selection unit selects the synchronization signal on a basis of amagnitude relationship of score information corresponding to asynchronization signal received from the other device.

(9)

The communication device according any one of (1) to (8), furtherincluding

a control unit configured to determine whether or not to transmit asynchronization signal after the acquisition of the synchronizationtiming by the synchronization processing unit on a basis of origininformation of a synchronization signal selected by the selection unit.

(10)

The communication device according to (9), in which

the origin information indicates a number of interposing devices in theprocedure of relaying the synchronization timing from a source device toa transmission source device of a synchronization signal selected by theselection unit, the source device serving as a source for asynchronization signal for acquisition of synchronization timing in thetransmission source device, and

the control unit determines not to transmit the synchronization signalin a case where a number of the devices exceeds a threshold value.

(11)

The communication device according to any one of (1) to (10), furtherincluding

an acquisition unit configured to acquire an ID for generating asynchronization signal received from the other device as the origininformation.

(12)

The communication device according to any one of (1) to (10), furtherincluding

an acquisition unit configured to acquire the origin information fromsystem information to be transmitted from the other device.

(13)

The communication device according to (2), in which

the selection unit decides which synchronization signal corresponding toorigin information to select in accordance with a movement condition ofthe communication device.

(14)

The communication device according to (13), in which

the selection unit uses a lane ID that indicates which road thecommunication device has moved along as a movement condition of thecommunication device.

(15)

The communication device according to (1), in which

the selection unit decides which synchronization signal corresponding toorigin information to select in accordance with an instruction from anexternal device.

(16)

The communication device according to (1), in which

the selection unit decides which synchronization signal corresponding toorigin information to select using information to be provided from anexternal device.

(17)

A communication device including:

a synchronization processing unit configured to acquire synchronizationtiming on a basis of reception of a synchronization signal; and

a control unit configured to control transmission of the synchronizationsignal after the acquisition of the synchronization timing by thesynchronization processing unit, in which

the control unit further controls transmission of origin informationthat indicates an origin of the synchronization signal used for theacquisition of the synchronization timing.

(18)

A communication method including:

selecting, by a processor, a synchronization signal from respectivesynchronization signals received from two or more other devices on abasis of origin information that is acquired by communication withanother device and that indicates an origin of a synchronization signalused for acquisition of synchronization timing in the other device; and

acquiring synchronization timing using the selected synchronizationsignal.

(19)

A communication method including:

acquiring synchronization timing on a basis of reception of asynchronization signal;

controlling transmission of a synchronization signal after theacquisition of the synchronization timing; and

controlling, by a processor, transmission of origin information thatindicates an origin of a synchronization signal used for the acquisitionof the synchronization timing.

REFERENCE SIGNS LIST

-   20 UE-   22 vehicle-   40 GPS satellite-   50 RSU-   210 communication unit-   220 Signal processing unit-   230 storage unit-   240 selection unit-   250 synchronization processing unit-   260 control unit-   310 communication unit-   330 storage unit-   360 control unit

The invention claimed is:
 1. A communication device comprising: aselection unit configured to select a synchronization signal fromrespective synchronization signals received from two or more otherdevices on a basis of origin information that is acquired bycommunication with another device and that indicates an origin of asynchronization signal used for acquisition of synchronization timing inthe other device; and a synchronization processing unit configured toacquire synchronization timing using the synchronization signal selectedby the selection unit, wherein the origin information includesinformation corresponding to a source device serving as a source of asynchronization signal for the acquisition of the synchronization timingin the other device, the selection unit recognizes a source devicecorresponding to a synchronization signal received from the other deviceon a basis of the origin information, and prioritize, among asynchronization signal corresponding to a first source device and asynchronization signal corresponding to a second source device accordingto a system that provides service in a wider range compared with thefirst source device, selection of the synchronization signalcorresponding to the second source device, the first source device is acellular base station, and the second source device is a GPS satellite.2. The communication device according to claim 1, wherein the origininformation includes information that indicates a procedure of relayingthe synchronization timing from the source device to the other device.3. The communication device according to claim 2, wherein the origininformation includes number-of-interpositions information that indicatesa number of interposing devices in the procedure of relaying thesynchronization timing from the source device to the other device. 4.The communication device according to claim 3, wherein the selectionunit recognizes a number of interposing devices in a relaying procedurecorresponding to a synchronization signal received from the other deviceon a basis of the number-of-interpositions information, and prioritize,among a synchronization signal corresponding to a first relayingprocedure and a synchronization signal corresponding to a second relayprocedure having a larger number of interposing devices compared withthe first relaying procedure, selection of the synchronization signalcorresponding to the first relaying procedure.
 5. The communicationdevice according to claim 1, wherein the origin information includesscore information calculated on a basis of the origin of thesynchronization signal used for acquisition of the synchronizationtiming in the other device, and the selection unit selects thesynchronization signal on a basis of a magnitude relationship of scoreinformation corresponding to a synchronization signal received from theother device.
 6. The communication device according to claim 1, furthercomprising a control unit configured to determine whether or not totransmit a synchronization signal after the acquisition of thesynchronization timing by the synchronization processing unit on a basisof origin information of a synchronization signal selected by theselection unit.
 7. The communication device according to claim 6,wherein the origin information indicates a number of interposing devicesin the procedure of relaying the synchronization timing from a sourcedevice to a transmission source device of a synchronization signalselected by the selection unit, the source device serving as a sourcefor a synchronization signal for acquisition of synchronization timingin the transmission source device, and the control unit determines notto transmit the synchronization signal in a case where a number of thedevices exceeds a threshold value.
 8. The communication device accordingto claim 1, further comprising an acquisition unit configured to acquirean ID for generating a synchronization signal received from the otherdevice as the origin information.
 9. The communication device accordingto claim 1, further comprising an acquisition unit configured to acquirethe origin information from system information to be transmitted fromthe other device.
 10. The communication device according to claim 2,wherein the selection unit decides which synchronization signalcorresponding to origin information to select in accordance with amovement condition of the communication device.
 11. The communicationdevice according to claim 10, wherein the selection unit uses a lane IDthat indicates which road the communication device has moved along as amovement condition of the communication device.
 12. The communicationdevice according to claim 1, wherein the selection unit decides whichsynchronization signal corresponding to origin information to select inaccordance with an instruction from an external device.
 13. Thecommunication device according to claim 1, wherein the selection unitdecides which synchronization signal corresponding to origin informationto select using information to be provided from an external device. 14.A communication method comprising: selecting, by a processor, asynchronization signal from respective synchronization signals receivedfrom two or more other devices on a basis of origin information that isacquired by communication with another device and that indicates anorigin of a synchronization signal used for acquisition ofsynchronization timing in the other device; and acquiringsynchronization timing using the selected synchronization signal,wherein the origin information includes information corresponding to asource device serving as a source of a synchronization signal for theacquisition of the synchronization timing in the other device, theselecting includes recognizing a source device corresponding to asynchronization signal received from the other device on a basis of theorigin information, and prioritize, among a synchronization signalcorresponding to a first source device and a synchronization signalcorresponding to a second source device according to a system thatprovides service in a wider range compared with the first source device,selection of the synchronization signal corresponding to the secondsource device, the first source device is a cellular base station, andthe second source device is a GPS satellite.